Migration of unified table metadata graph nodes

ABSTRACT

Metadata is stored within a database for each of a plurality of objects in different frames associated with a structure descriptor (e.g., a container directory entry, etc.). The frames are part of a metadata page and each comprising an object and a header specifying a version identifier for the object and a size of the object. The structure descriptor initially is built for a first build identifier. Thereafter, upon the structure descriptor changing from the first build identifier to a second build identifier, at least one of the objects that require migration is identified. The identification is based on the version identifier for the object being different from the second build identifier. In response, the identified objects are migrated from their corresponding frame to a new frame. The new frame includes the objects and new headers that include a version identifier equal to the second build identifier.

TECHNICAL FIELD

The subject matter described herein relates to the migration of table metadata graph nodes as part of a database version change.

BACKGROUND

With some database systems, data objects forming part of the database can take various forms. In some cases, after an upgrade or other structural change (such as changes in number of rows, columns, etc.), some objects can be compatible with such changes while other objects may be obsolete. These latter objects must be modified or otherwise changed in order for the upgrade to be effectively implemented.

SUMMARY

In one aspect, metadata is stored within a database for each of a plurality of objects in different frames associated with a structure descriptor (e.g., a container directory entry, etc.). The frames are part of a metadata page and each comprising an object and a header specifying a version identifier for the object and a size of the object. The structure descriptor initially is built for a first build identifier. Thereafter, upon the structure descriptor changing from the first build identifier to a second build identifier, at least one of the objects that require migration is identified. The identification is based on the version identifier for the object being different from the second build identifier. In response, the identified objects are migrated from their corresponding frame to a new frame. The new frame includes the objects and new headers that include a version identifier equal to the second build identifier.

Frames from which the identified objects have been migrated can be deactivated after completion of the migration. Each header can further specify a size of the corresponding object. The identified objects can be modified to be compatible with the second build identifier. The identified objects can be modified prior to the migration and/or as part of the migration. The version identifier for the object can be less than the second build identifier.

A first object can be migrated from a first frame to a second frame by generating a second object in the second frame that is larger than the first object and subsequently populating data encapsulated in the first object to the second object.

The database can be an in-memory database such as a column-oriented database that stores data tables as sections of columns.

Non-transitory computer program products (i.e., physically embodied computer program products) are also described that store instructions, which when executed by one or more data processors of one or more computing systems, causes at least one data processor to perform operations herein. Similarly, computer systems are also described that may include one or more data processors and memory coupled to the one or more data processors. The memory may temporarily or permanently store instructions that cause at least one processor to perform one or more of the operations described herein. In addition, methods can be implemented by one or more data processors either within a single computing system or distributed among two or more computing systems. Such computing systems can be connected and can exchange data and/or commands or other instructions or the like via one or more connections, including but not limited to a connection over a network (e.g. the Internet, a wireless wide area network, a local area network, a wide area network, a wired network, or the like), via a direct connection between one or more of the multiple computing systems, etc.

The subject matter described herein provides many technical advantages. For example, the current subject matter allows for objects to be efficiently migrated as part of a database build upgrade.

The details of one or more variations of the subject matter described herein are set forth in the accompanying drawings and the description below. Other features and advantages of the subject matter described herein will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating features of a business software system architecture;

FIG. 2 is another diagram illustrating features of a business software system architecture;

FIG. 3 is a schematic representation of fragments stored in a main store;

FIG. 4 is a diagram illustrating features of a unified table container page chain;

FIG. 5 is a diagram illustrating features of a unified table delta;

FIG. 6 is a diagram illustrating features of a unified table unsorted dictionary;

FIG. 7 is a functional block diagram illustrating performing a delta merge operation and a read operation using a unified table;

FIG. 8 is a diagram illustrating a metadata page including a plurality of frames; and

FIG. 9 is a process flow diagram illustrating migration of unified table metadata graph nodes.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

The current subject matter includes a number of aspects that can be applied individually or in combinations of one or more such aspects to support a unified database table approach that integrates the performance advantages of in-memory database approaches with the reduced storage costs of on-disk database approaches. The current subject matter can be implemented in database systems using in-memory OLAP, for example including databases sized at several terabytes (or more), tables with billions (or more) of rows, and the like; systems using in-memory OLTP (e.g. enterprise resource planning or ERP system or the like, for example in databases sized at several terabytes (or more) with high transactional volumes; and systems using on-disk OLAP (e.g. “big data,” analytics servers for advanced analytics, data warehousing, business intelligence environments, or the like), for example databases sized at several petabytes or even more, tables with up to trillions of rows, and the like.

The current subject matter can be implemented as a core software platform of an enterprise resource planning (ERP) system, other business software architecture, or other data-intensive computing application or software architecture that runs on one or more processors that are under the control of a specific organization. This arrangement can be very effective for a large-scale organization that has very sophisticated in-house information technology (IT) staff and for whom a sizable capital investment in computing hardware and consulting services required to customize a commercially available business software solution to work with organization-specific business processes and functions is feasible. FIG. 1 shows a diagram 100 of a system consistent with such an implementation. A computing system 110 can include one or more core software platform modules 120 providing one or more features of the business software system. The computing system can also aggregate or otherwise provide a gateway via which users can access functionality provided by one or more external software components 130. Client machines 140 can access the computing system, either via a direct connection, a local terminal, or over a network 150 (e.g. a local area network, a wide area network, a wireless network, the Internet, or the like).

A database management agent 160 or other comparable functionality can access a database management system 170 that stores and provides access to data (e.g. definitions of business scenarios, business processes, and one or more business configurations as well as data, metadata, master data, etc. relating to definitions of the business scenarios, business processes, and one or more business configurations, and/or concrete instances of data objects and/or business objects that are relevant to a specific instance of a business scenario or a business process, and the like. The database management system 170 can include at least one table 180 and additionally include parallelization features consistent with those described herein.

FIG. 2 shows a block diagram of an architecture 200 illustrating features that can be included in a database or database management system consistent with implementations of the current subject matter. A table data store 202, which can be retained among a plurality of data volumes 204, can include one or more of a delta store 206 (e.g. a paged delta part, which can optionally be OLTP optimized and can optionally include a merge process 208), an index store 212 (e.g. one or more segmented indices), and a main store 210. The main store 210 can include a main part that is fragmented consistent with features described herein.

To achieve a best possible compression and also to support very large data tables, a main part of the table can be divided into one or more fragments. FIG. 3 shows a schematic representation 300 of the various fragments stored in main store 210. One or more main fragments or fragments 330 can be used for each table or column of a database. Small, manageable tables can be represented with a single fragment. Very large tables can be split into two or more table partitions 335. Each table partition may, in turn, include two or more fragments 330. Fragments 330 can be horizontal slices of the table to which they belong. Each fragment 330 can include one or more column fragments 340. Each column fragment 340 can have its own dictionary and value ID array consistent with the features described herein.

Fragments 330 can advantageously be sufficiently large to gain maximum performance due to optimized compression of the fragment and high in-memory performance of aggregations and scans. Conversely, such fragments can be sufficiently small to load a largest column of any given fragment into memory and to sort the fragment in-memory. Fragments can also be sufficiently small to be able to coalesce two or more partially empty fragments into a smaller number of fragments. As an illustrative and non-limiting example of this aspect, a fragment can contain one billion rows with a maximum of 100 GB of data per column. Other fragment sizes are also within the scope of the current subject matter. A fragment can optionally include a chain of pages. In some implementations, a column can also include a chain of pages. Column data can be compressed, for example using a dictionary and/or any other compression method. Table fragments can be materialized in-memory in contiguous address spaces for maximum performance. All fragments of the database can be stored on-disk, and access to these fragments can be made based on an analysis of the data access requirement of a query.

Referring again to FIG. 2, other parts of the architecture 200 can include a data manipulation language (DML) handling module or similar functionality 214, one or more query handling modules or similar functionality 216 (e.g. including multi-version concurrency control), an index builder 220 that supports the index store 212, a query language engine 222 (which can, for example, be a SQL engine), a complex events processing module (e.g. an event handler, a stream processing module, etc.) 224 for receiving inputs from a user 226, and the like.

FIG. 4 shows a block diagram illustrating an example of a unified table container page chain 400. As described above, each fragment can optionally include a chain of pages. In general, a container can be represented as a page chain. A page chain can generally be characterized as a set of pages that are linked in a given order. The term pages, as used herein, refers to a basic unit of storage in a database. A page size is generally established when the database is built and typically cannot be changed. A representative page size can be on the order of 2 kB, 4 kB, 8 kB, 16 kB, or the like. Once the server is built, the value usually cannot be changed. Different types of pages can store different types of database objects. For example, data pages can store data rows or columns for a table. Index pages can store index rows for one or more levels of an index. Large object (LOB) pages can store data for text and image columns, for Java off-row columns, and the like.

Also as shown in FIG. 4, sub-chains of the page chain can be defined for a delta part, a main part, dictionaries, index segments (optionally, not shown in FIG. 2), and the like such that a “whole” of each of these entities contains one or more pages. In some implementations of the current subject matter, a delta part can include both “hot” delta fragments 402 and “cold” delta fragments 404, which can be stored separately. The main part can also be subdivided into main fragments 330. Pages containing dictionary-compressed columnar data 410 can refer to pages containing dictionaries for them. Individual table parts can be loaded into main memory on-demand. A merge process can be decoupled from transaction handling such that a merge process can be executed at recovery time (e.g. during log replay). A page chain, such as the example shown in FIG. 4, can be initiated by a container directory entry (CDE) 412.

A single RowID space can be used across pages in a page chain. A RowID, which generally refers to a logical row in the database, can be used to refer to a logical row in an in-memory portion of the database and also to a physical row in an on-disk portion of the database. A row index typically refers to physical 0-based index of rows in the table. A 0-based index can be used to physically address rows in a contiguous array, where logical RowIDs represent logical order, not physical location of the rows. In some in-memory database systems, a physical identifier for a data record position can be referred to as a UDIV or DocID. Distinct from a logical RowID, the UDIV or DocID (or a comparable parameter) can indicate a physical position of a row (e.g. a data record), whereas the RowID indicates a logical position. To allow a partition of a table to have a single RowID and row index space consistent with implementations of the current subject matter, a RowID can be assigned a monotonically increasing ID for newly-inserted records and for new versions of updated records across fragments. In other words, updating a record will change its RowID, for example, because an update is effectively a deletion of an old record (having a RowID) and insertion of a new record (having a new RowID). Using this approach, a delta store of a table can be sorted by RowID, which can be used for optimizations of access paths. Separate physical table entities can be stored per partition, and these separate physical table entities can be joined on a query level into a logical table.

When an optimized compression is performed during a columnar merge operation to add changes recorded in the delta store to the main store, the rows in the table are generally re-sorted. In other words, the rows after a merge operation are typically no longer ordered by their physical row ID. Therefore, stable row identifier can be used consistent with one or more implementations of the current subject matter. The stable row identifiers can optionally be a logical RowID. Use of a stable, logical (as opposed to physical) RowID can allow rows to be addressed in REDO/UNDO entries in a write-ahead log and transaction undo log. Additionally, cursors that are stable across merges without holding references to the old main version of the database can be facilitated in this manner. To enable these features, a mapping of an in-memory logical RowID to a physical row index and vice versa can be stored. In some implementations of the current subject matter, a RowID column can be added to each table. The RowID column can also be amenable to being compressed in some implementations of the current subject matter.

FIG. 5 shows a block diagram of a unified table delta 500 consistent with one or more implementations of the current subject matter. In some examples, a “hot” and “cold” delta approach can be used in which uncompressed data are retained in the “hot” delta part, while dictionary-compressed data are retained in the “cold” delta part with a mini-merge performed between the hot and cold parts. Such a delta part can be considered as a single container. As shown in FIG. 5, each delta sub-chain can have its own transient structure. In other words, a separate structure can be used for each delta. A page vector 502 can hold page handles to individual pages 504 and can allow a fast iteration over the pages 504 (for example as part of a column or table scan). A page handle to an individual page 504 can include a pin or the like held in memory. As used herein, the term “pin” refers to holding a particular data page (which may also have been stored on disk) in memory. As an example, if a page is not pinned, it can be cleared from memory. Pinning is typically done on data pages being actively accessed so as to avoid potential performance degradations associated with reading the page from disk into memory.

A RowID index 506 can serve as a search structure to allow a page 504 to be found based on a given interval of RowID values. The search time can be on the order of log n, where n is very small. The RowID index can provide fast access to data via RowID values. For optimization, “new” pages can have a 1:1 association between RowID and row index, so that simple math (no lookup) operations are possible. Only pages that are reorganized by a merge process need a RowID index in at least some implementations of the current subject matter.

FIG. 6 shows a block diagram of a unified table unsorted dictionary 600. Consistent with one or more implementations of the current subject matter, column data in a delta part can use unsorted dictionaries. A transient structure can be provided per delta column dictionary. The page vector 502 can handle pinning of pages in memory. Direct access can be provided via a pointer from other structures. A value vector indirection 602 can allow a same number of values per dictionary block 604. This capability can support an order of 1 performance cost for lookup of a value by ValueID. A dictionary can assign a unique ValueID (typically a numeric value) to each unique value such that the unique values (which are typically larger in memory size than the ValueID) can be stored once rather than multiple times. A value array is a structure used by the dictionary to retrieve values given a ValueID or vice versa. This technique, which can reduce the amount of memory needed to store a set of values where the values are not unique, is typically referred to as dictionary compression. A Value to ValueID map 606 can support hash or B-tree sizes on the order of 1 or on the order of log n for lookup of ValueID by value. A B-tree is a tree data structure that keeps data sorted and allows searches, sequential access, insertions, and deletions in logarithmic time. This capability can be necessary for dictionary compression. A B-tree can be better for range scans but can be more expensive to maintain.

FIG. 7 shows a functional block diagram 700 for performing a delta merge operation 710 on a unified table. New transactions or changes can initially be written into delta store 206. Main store 210 can include one active fragment 712 and one or more closed fragments 716. When updates are merged from delta store 206 into the main store 210, existing records in the closed fragments 716 cannot be changed. Instead, new versions of the records can be added to the active fragment 712, and old versions can be marked as invalid.

Functional block diagram 700 also illustrates a read operation 720. Generally, read operations can have access to all fragments (i.e., active fragment 712 and closed fragments 716). Read operations can be optimized by loading only the fragments that contain data from a particular query. Fragments that do not contain such data can be excluded. In order to make this decision, container-level metadata (e.g., a minimum value and/or a maximum value) can be stored for each fragment. This metadata can be compared to the query to determine whether a fragment contains the requested data.

With reference to diagram 800 of FIG. 8, the container directory entry (412) can be linked to a plurality of frames 820 that form part of a metadata page 810. Metadata pages describe how unified tables (UT) are composed, e.g. how many columns they have, of which type these columns are, and can contain logical pointers to page chains which contain the data. As a table contains multiple fragments and these fragments contain columns, for all these objects (columns, fragments, etc.) there can be structure descriptors that describe that certain objects and some of these structure descriptors do contain a (logical) pointer to some other structure descriptor, forming a tree of meta data which describes the whole UT. In addition, the CDE 412 can include a map or otherwise have an associated build ID which references the particular version of the database build. Each frame 820 can include a header 830 and an object 840. The header 830 can encapsulate information such as a class identifier, version, and size of the corresponding object 840. The CDE 412 can map each object 840 to a pointer that refers to the corresponding frame 820.

If the database build changes, the build ID for the structure descriptor (e.g., CDE 412, etc.) may need to be migrated (e.g., CDE 412, etc.). The build ID for some structure descriptor changes if the descriptor is changed (e.g. a developer modified, etc. it) but not necessarily with any new build of the database. Migrating to a newer version of the database does not automatically include a migration of all structure descriptors. The descriptors need to be checked but most of them will probably remain unchanged.

In some cases, the objects 840 will also require updating so that they are compatible with the build ID. For example, the update can sometimes require that the objects 840 are modified so that they are larger. This determination can be made by comparing the version value in the header 830 with the current build ID. If the version value is equal or greater than the build ID, in some cases, no changes are needed. Stated differently, if the IDs are identically no change is needed. If the ID of the structure descriptor is greater than the build ID of the database it would result in starting an old version of the database with a persistency created with a newer version of the database. That scenario can be prohibited by at startup. However, if the version value is less than the current build ID, changes are required. Such changes can be implemented through a migration operation.

As one example, object 840 ₂ (in frame 820 ₂) is determined to require migration because the corresponding version is less than the build ID of the CDE 412. Thereafter, a new frame 820 ₅ can be generated. Next, a header 830 ₅ and a new object 840′₂ can be created in the new frame 820 ₅. The new object 840′₂ is larger than the original object 840 ₂ (as is required by the new build). The contents of the original object 840 ₂ can be populated into the new object 840′₂. Thereafter, the original object can be deactivated. In addition, the pointer in the map of the CDE 412 can then be changed from the original object 840 ₂ to the new object 840′₂.

In some variations, each object 840 can include structure descriptors. These structure descriptors can include, for example, an integer (representing, for example, columns, number of values in the dictionary, etc.), a pointer (pointer either to some other structure descriptor or to a page chain containing the data), and a string reference (e.g., the name of the column, etc.) These structure descriptors can be used so that one object 840 can directly reference another object 840. Structure descriptors describe the structure of some database object (e.g., how many columns it has, of which type the columns are, where to find the contained data, etc.).

With reference to diagram 900 of FIG. 9, at 910, metadata can be stored within a database for each of a plurality of objects in different frames of a structure descriptor (e.g., container directory entry, etc.). The frames form part of a metadata page and each include an object and a header specifying a version identifier for the object and a size of the object. The structure descriptor initially is for a first build identifier. Subsequently, at 920 and upon the container directory entry changing from the first build identifier to a second build identifier, at least one of the objects is identified that requires migration. This identification can be based on the version identifier for the object being different from the second build identifier. Next, at 930, the identified objects are migrated from their corresponding frame to a new frame. The new frames each include the objects and new headers that include a version identifier equal to the second build identifier. Optionally, at 940, the frames from which the identified objects have been migrated can be deactivated after completion of the migration.

One or more aspects or features of the subject matter described herein can be realized in digital electronic circuitry, integrated circuitry, specially designed application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs) computer hardware, firmware, software, and/or combinations thereof. These various aspects or features can include implementation in one or more computer programs that are executable and/or interpretable on a programmable system including at least one programmable processor, which can be special or general purpose, coupled to receive data and instructions from, and to transmit data and instructions to, a storage system, at least one input device, and at least one output device. The programmable system or computing system may include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other.

These computer programs, which can also be referred to as programs, software, software applications, applications, components, or code, include machine instructions for a programmable processor, and can be implemented in a high-level procedural language, an object-oriented programming language, a functional programming language, a logical programming language, and/or in assembly/machine language. As used herein, the term “machine-readable medium” refers to any computer program product, apparatus and/or device, such as for example magnetic discs, optical disks, memory, and Programmable Logic Devices (PLDs), used to provide machine instructions and/or data to a programmable processor, including a machine-readable medium that receives machine instructions as a machine-readable signal. The term “machine-readable signal” refers to any signal used to provide machine instructions and/or data to a programmable processor. The machine-readable medium can store such machine instructions non-transitorily, such as for example as would a non-transient solid-state memory or a magnetic hard drive or any equivalent storage medium. The machine-readable medium can alternatively or additionally store such machine instructions in a transient manner, such as for example as would a processor cache or other random access memory associated with one or more physical processor cores.

To provide for interaction with a user, one or more aspects or features of the subject matter described herein can be implemented on a computer having a display device, such as for example a cathode ray tube (CRT) or a liquid crystal display (LCD) or a light emitting diode (LED) monitor for displaying information to the user and a keyboard and a pointing device, such as for example a mouse or a trackball, by which the user may provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well. For example, feedback provided to the user can be any form of sensory feedback, such as for example visual feedback, auditory feedback, or tactile feedback; and input from the user may be received in any form, including, but not limited to, acoustic, speech, or tactile input. Other possible input devices include, but are not limited to, touch screens or other touch-sensitive devices such as single or multi-point resistive or capacitive trackpads, voice recognition hardware and software, optical scanners, optical pointers, digital image capture devices and associated interpretation software, and the like.

In the descriptions above and in the claims, phrases such as “at least one of” or “one or more of” may occur followed by a conjunctive list of elements or features. The term “and/or” may also occur in a list of two or more elements or features. Unless otherwise implicitly or explicitly contradicted by the context in which it is used, such a phrase is intended to mean any of the listed elements or features individually or any of the recited elements or features in combination with any of the other recited elements or features. For example, the phrases “at least one of A and B;” “one or more of A and B;” and “A and/or B” are each intended to mean “A alone, B alone, or A and B together.” A similar interpretation is also intended for lists including three or more items. For example, the phrases “at least one of A, B, and C;” “one or more of A, B, and C;” and “A, B, and/or C” are each intended to mean “A alone, B alone, C alone, A and B together, A and C together, B and C together, or A and B and C together.” In addition, use of the term “based on,” above and in the claims is intended to mean, “based at least in part on,” such that an unrecited feature or element is also permissible.

The subject matter described herein can be embodied in systems, apparatus, methods, and/or articles depending on the desired configuration. The implementations set forth in the foregoing description do not represent all implementations consistent with the subject matter described herein. Instead, they are merely some examples consistent with aspects related to the described subject matter. Although a few variations have been described in detail above, other modifications or additions are possible. In particular, further features and/or variations can be provided in addition to those set forth herein. For example, the implementations described above can be directed to various combinations and subcombinations of the disclosed features and/or combinations and subcombinations of several further features disclosed above. In addition, the logic flows depicted in the accompanying figures and/or described herein do not necessarily require the particular order shown, or sequential order, to achieve desirable results. Other implementations may be within the scope of the following claims. 

What is claimed is:
 1. A method comprising: storing, within an in-memory database, a metadata page describing a composition of a unified table, the unified table comprising a plurality of columns of data, each column having a column type, data for each column stored in at least one page chain, the metadata page comprising a plurality of structure descriptors forming a tree of metadata corresponding to the structure of the unified table, the metadata page further comprising metadata for each of a plurality of objects in different frames associated with one of the plurality of structure descriptors describing a database structure of the corresponding object, the different frames being part of the metadata page, each different frame comprising an object and a header specifying a version identifier for the object and a size of the object, the plurality of structure descriptors initially being for a first build identifier, wherein the plurality of objects comprises columns of data; identifying, upon the plurality of structure descriptors changing from the first build identifier to a second build identifier, at least one of the objects that requires migration, the identification being based on the version identifier for the object being different from the second build identifier; migrating only the objects from their corresponding frame to a new frame in the in-memory database, the new frame including the objects and new headers that include a version identifier equal to the second build identifier, wherein each object is migrated from its corresponding frame to the new frame by generating a corresponding new object in the new frame that is larger than the object, and subsequently populating data encapsulated in the object to the new object in the new frame; and deactivating the different frames from which the objects have been migrated after completion of the migration.
 2. The method of claim 1 further comprising: modifying the objects to be compatible with the second build identifier.
 3. The method of claim 2, wherein the objects are modified prior to the migration.
 4. The method of claim 2, wherein the objects are modified as part of the migration.
 5. The method of claim 1, wherein the version identifier for the object is less than the second build identifier.
 6. The method of claim 1, wherein the in-memory database is a column-oriented database that stores data tables as sections of columns.
 7. A non-transitory computer program product storing instructions which, when executed by at least one hardware data processor forming part of at least one computing system, result in operations comprising: storing, within an in-memory database, a metadata page describing a composition of a unified table, the unified table comprising a plurality of columns of data, each column having a column type, data for each column stored in at least one page chain, the metadata page comprising a plurality of structure descriptors forming a tree of metadata corresponding to the structure of the unified table, the metadata page further comprising metadata for each of a plurality of objects in different frames associated with one of the plurality of structure descriptors describing a database structure of the corresponding object, the different frames being part of the metadata page, each different frame comprising an object and a header specifying a version identifier for the object and a size of the object, the plurality of structure descriptors initially being for a first build identifier, wherein the plurality of objects comprises columns of data; identifying, upon the plurality of structure descriptors changing from the first build identifier to a second build identifier, at least one of the objects that requires migration, the identification being based on the version identifier for the object being different from the second build identifier; migrating only the objects from their corresponding frame to a new frame in the in-memory database, the new frame including the objects and new headers that include a version identifier equal to the second build identifier, wherein each object is migrated from its corresponding frame to the new frame by generating a corresponding new object in the new frame that is larger than the object, and subsequently populating data encapsulated in the object to the new object in the new frame; and deactivating the different frames from which the objects have been migrated after completion of the migration.
 8. The non-transitory computer program product of claim 7, wherein the operations further comprise: modifying the objects to be compatible with the second build identifier.
 9. The non-transitory computer program product of claim 8, wherein the objects are modified prior to the migration.
 10. The non-transitory computer program product of claim 8, wherein the objects are modified as part of the migration.
 11. The non-transitory computer program product of claim 7, wherein the version identifier for the object is less than the second build identifier.
 12. The non-transitory computer program product of claim 7, wherein the in-memory database stores data tables as sections of columns.
 13. A system comprising: at least one hardware data processor; and memory storing instructions which, when executed by the at least one hardware data processor, result in operations comprising: storing, within an in-memory database, a metadata page describing a composition of a unified table, the unified table comprising a plurality of columns of data, each column having a column type, data for each column stored in at least one page chain, the metadata page comprising a plurality of structure descriptors forming a tree of metadata corresponding to the structure of the unified table, the metadata page further comprising metadata for each of a plurality of objects in different frames associated with one of the plurality of structure descriptors describing a database structure of the corresponding object, the different frames being part of the metadata page, each different frame comprising an object and a header specifying a version identifier for the object and a size of the object, the plurality of structure descriptors initially being for a first build identifier, wherein the plurality of objects comprises columns of data; identifying, upon the plurality of structure descriptors changing from the first build identifier to a second build identifier, at least one of the objects that requires migration, the identification being based on the version identifier for the object being different from the second build identifier; migrating only the objects from their corresponding frame to a new frame in the in-memory database, the new frame including the objects and new headers that include a version identifier equal to the second build identifier, wherein each object is migrated from its corresponding frame to the new frame by generating a corresponding new object in the new frame that is larger than the object, and subsequently populating data encapsulated in the object to the new object in the new frame; and deactivating the different frames from which the objects have been migrated after completion of the migration.
 14. The method of claim 1, wherein the plurality of structure descriptors describing a database structure of the corresponding object comprises at least one of: a number of columns, a type of column, a location in the database structure, a pointer to another one of the plurality of structure descriptors, and a pointer to a page chain. 